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In 2017, NASA's Fermi Gamma-ray Space Telescope connected

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gamma rays, the highest-energy form of light, with new

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cosmic messengers--gravitational waves and high-energy neutrinos.

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For the first time, the discoveries linked these new signals to

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the one sky watchers have known for millennia -- light.

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First, gravitational waves and gamma rays were emitted from merging neutron

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stars. Fermi saw the first-ever light detected from

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a gravitational wave event. Then, just weeks later, Fermi

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connected a high-energy neutrino seen by the IceCube experiment at the

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South Pole to a black-hole-powered galaxy, which fires a jet of matter

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that emits both neutrinos and gamma rays. This is no

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overnight success story. The origins of both these breakthroughs

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span more than a century. As the

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19th century closed. scientists worked to understand many new phenomena

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including radioactivity, and new forms of light --

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X-rays and gamma rays. Light was expected to need a medium, called

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the "aether," in order to move through space, which meant its speed should change when measured

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in different directions on the moving Earth. Yet no changes were seen.

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Solving this puzzle led to Einstein's special theory

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of relativity, which assumed light in a vacuum moves at a constant speed that

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nothing can exceed. His theory formed a theoretical basis for

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particle physics... ...which in 1912 incorporated an unexpected

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source -- a rain of particles from space called cosmic rays.

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Einstein's general theory of relativity, his theory

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of gravity, regarded space-time as the fabric of the cosmos.

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Space-time tells matter how to move, and matter tells space-time how to

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curve. As scientists probed the subatomic

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realm, one type of radioactive decay suggested the presence

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of a new lightweight particle, dubbed the "neutrino."

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Later, Einstein and Nathan Rosen showed

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that accelerating masses can create gravitational waves that ripple

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across space-time.

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Following World War II, technological advances permitted new kinds

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of observations. In the mid-Fifties, neutrinos were detected for the

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first time. Richard Feynman showed that gravitational waves must

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move matter, which means they're detectable. In a few years, the first

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efforts to do so began. The 1960s brought

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the first gamma rays seen in space, the first neutrinos

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detected from the Sun's interior, and something new -- later called

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gamma-ray bursts, or GRBs -- was caught by satellites looking for banned

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tests of nuclear weapons. In 1971,

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Rainer Weiss conceived of a way to detect gravitational waves

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using lasers, one of the roots of LIGO.

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1987 delivered the brightest supernova in nearly 400

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years. Three experiments caught neutrinos from the star's collapse.

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Instruments on balloons saw gamma rays from radioactive elements

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in the explosion's debris. The 1990s

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and 2000s brought: new satellites for exploring the

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gamma-ray universe; the construction and first operation of LIGO;

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and AMANDA, a neutrino detector built under the ice at the South Pole.

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In 2005,

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NASA's Swift satellite showed that short gamma-ray bursts likely come

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from merging neutron stars. Soon after,

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NASA launched Fermi, providing our best-ever view of the gamma-ray sky.

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AMANDA morphed into IceCube, which was completed in 2010.

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It monitors a cubic kilometer of ice under the South Pole

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for neutrinos. The same year, LIGO shut down

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for years of upgrades. IceCube reported more than

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two dozen high-energy neutrinos -- likely arrivals from

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beyond our galaxy. In 2015, the upgraded LIGO

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saw the first gravitational waves. The source: merging black holes

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over a billion light-years away. And in 2017,

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gamma-ray counterparts accompanied both a gravitational wave

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event and a cosmic neutrino source.

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Multimessenger astronomy -- and its promise of greater insight into the most

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powerful processes in the universe -- has arrived.

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[Music]

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[Music]

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[NASA Astrophysics]

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[Beeping]

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[Beeping]

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[Beeping]